Step-by-step installation of Grundfos circulation pump

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Installation of a Grundfos circulation pump step by step – complete practical guide

Replacing or installing a circulation pump for the first time is one of those tasks that a skilled DIY enthusiast can manage, but only if they know exactly what they are doing and why. From experience, I know that many problems do not arise during the installation itself, but even before it – due to a wrong pump selection, incorrect measurements, or simply forgetting to drain the water before loosening the flange. This guide is therefore not only about turning a bolt, but about the entire process – from preparing the tools and diagnosing the old pump to setting the pressure, bleeding the system and the first test run.

Before reading this article, you may also find our article How to choose the right Grundfos circulation pump for heating and What Grundfos pump power do I need for my house helpful – if you are not yet sure whether you are buying the right model, start there.

Why to change a circulation pump and when is the right time

A standard circulation pump lasts 15 to 20 years with proper maintenance. In practice, however, I often encounter people who change the pump only when it completely stops working – and that usually happens at the worst possible moment, such as in January at midnight. The signals that indicate the end of the pump are clear if you know what to look for:

Increased noise – grinding, humming, vibrations, knocking. Bearings are worn out, the rotor may be clogged with deposits.
Radiators are not heating evenly – some are cold, others hot. The pump cannot maintain the flow.
Increased electricity consumption without an obvious reason. Old pumps with energy efficiency class E or G consume up to 5 times more than modern electronically controlled models.
Visible water leaks at the flange or at the shaft seal.
The pump does not start – the rotor is jammed after a long period of inactivity (typically after the summer shutdown).

If your pump is more than 15 years old and shows any of these symptoms, replacement is simply worth it – and that is also from an economic point of view. A modern electronically controlled pump, such as Grundfos UPS 25-30, consumes 30–60 W during normal operation in a family house instead of 100–150 W of an old analog model.

What you will need – tools, materials and safety

Installing a circulation pump is not complicated, but it requires preparation. Improvising when working with hot water and electricity is not a good idea.

List of tools

Adjustable wrench or a set of ring wrenches (24, 27, 30, 32 mm – depends on the flange size)
Hex keys (if the pump has locking screws)
Flat and cross screwdrivers
Digital multimeter (for measuring voltage and resistance)
Bucket, rags, hose for draining water
Teflon tape or hemp sealing compound + sealant
New flange gasket (rubber O-ring or flat gasket)
Clean cloth and WD-40 for loosening rusted screws
Level (spirit level) – not everyone remembers this, but the pump must be in the correct position

Safety first

Before any work on the heating system, there are a few rules that should not be ignored:

Disconnect the pump from the electrical network. It is not enough to switch it off with a switch – unplug the plug or turn off the corresponding circuit breaker in the distribution board and mark it so that no one accidentally turns it on.
Let the system cool down. If you are heating, wait at least 2–3 hours after turning off the boiler. The water in the system can have a temperature of 70–85 °C during full operation. A burn when opening the flange is a real risk.
Close the shut-off valves before and after the pump (if installed). If not, you will have to drain the entire system.
The pressure in the system must be zero. Check the pressure gauge on the boiler – it should indicate 0 bar, or at least close to zero, before loosening the flange.

Where in the system should the pump be and what about the installation direction

This is one of the most common sources of mistakes during installation. A circulation pump is typically installed on the return line – that is, on the pipe that carries the cooled water from the radiators back to the boiler. The reason is simple: lower temperature prolongs the life of the pump and seals. The temperature on the return line is typically 50–60 °C compared to 70–85 °C on the boiler outlet.

There are situations where the pump is installed on the supply branch – for example, in some solar systems or in underfloor heating with separate circuit division. In such cases, the pump must be certified for the corresponding temperature. For example, Grundfos Solar 25-120 is specifically designed for solar circuits, where temperatures can exceed 110 °C.

Motor orientation – horizontal or vertical?

Most older pumps (e.g., UPS series) must have the rotor axis in a horizontal position – this means that the terminal box and motor are on the side, not up or down. If the motor is oriented vertically upwards or downwards, the bearings would not be properly lubricated and the pump would wear out quickly.

Modern wet rotor pumps with permanent magnets (e.g. Grundfos ALPHA or Magna series) are more flexible in this respect and can handle various mounting angles – always check the installation manual for the specific model, however.

Practical rule: the terminal block of the electrical connection must point to the side or upwards, never directly downwards (risk of water entering the electrical part).

Step 1 – Preparation, closing the valves and draining

Before you touch the first screw, you need to prepare the system. The procedure is as follows:

1.1 Turn off the boiler. On a gas boiler, press the shut-off button or set the thermostat to minimum. On a solid fuel boiler, let the fuel burn out and wait for it to cool down – patience is truly essential here.

1.2 Close the valves before and after the pump. Most modern installations have ball valves directly at the pump. Turn them 90° – the lever is perpendicular to the pipe = closed. While doing so, also check whether the valves are sealing – after loosening the flange, you will see whether water is dripping or not.

1.3 If there are no valves available, drain the entire system. Every boiler has a drain cock usually at the lowest point of the system. Connect a hose, lead it to the sewer or a bucket, and open the cock. Open also the air vents on the radiators – this will speed up the draining and prevent air pockets from forming.

1.4 Check the pressure gauge. When the pressure drops to 0 bar, you can work safely. Never open a flange under pressure – even 0.5 bar can spray boiling water into your face.

1.5 Disconnect the electricity. Unplug the pump’s plug, or switch off the circuit breaker and mark it with a piece of tape with the inscription “DO NOT SWITCH ON – work on the system is in progress.” Verification: use a multimeter to check that there is no voltage on the pump’s terminals.

Step 2 – Dismantling the old pump

Now it is time for physical work. Sometimes it is harder to dismantle the old installation than to mount a new one – screws are often rusted, and flanges are glued with old gaskets.

2.1 Loosening the terminal block screw. Before loosening the flange, disconnect the electrical wiring. Grundfos UPS series usually have a cover on top of the terminal block – unscrew it, note or photograph the wiring (phase, neutral, ground), and unscrew the wires.

2.2 Loosening the flange. On most Grundfos UPS pumps, there are 4 screws or M10 or M12 socket head bolts. Use a key of the correct size – a box spanner is suitable, but risky – better are open-end wrenches. Loosen the screws diagonally (not in a circle), so the flange does not twist.

2.3 Be careful of residual water. Even if you have drained the system, there is usually 0.5–2 liters of water left in the pump loop. Have a bucket and a cloth ready. Loosen the flange slowly – if water starts to flow, let it drain in a controlled manner.

2.4 Removing the old pump. After loosening both flanges (inlet and outlet), you can pull out the pump. The old gasket usually remains stuck to the pipe flange – remove it with a scraper or a flat screwdriver. Clean the flange surface thoroughly – remnants of the old gasket cause water leaks in the new pump.

Step 3 – Preparation and selection of the replacement pump

Before buying a new pump, check the following parameters of the old one:

Flange size – the measured distance between the centers of the screws (type DN 25/Rp 1" or DN 32/Rp 5/4"). The standard distance between flanges (construction length) for the Grundfos UPS 25 series is 130 mm, for larger models 180 mm.
Maximum flow and head – you can find them on the label of the old pump or in its documentation.
Power supply – 230 V / 50 Hz is standard for family homes. Larger pumps may require 3× 400 V.
Type of flange thread – most Grundfos UPS have a flange connection Rp (cylindrical internal thread). Distinguish it from the G thread (also cylindrical, but a different standard).

If you are looking for a reliable and economically advantageous solution for a standard family house with central heating, the Grundfos UPS 25-30 will cover most common applications with a flow rate up to 3.5 m³/h and a head of 3 m. For a solar circuit or a system with a larger pipe loop, I recommend looking at the Grundfos Solar 15-80 or the more powerful Grundfos Solar 25-120.

More about choosing between pump types can be found in the articles Grundfos UPS vs. Grundfos solar pumps – which one is suitable for your system and Grundfos solar pumps – what they are used for and how they work.

Step 4 – Installation of the new Grundfos pump

Now it is time for the actual installation. Proceed systematically – each step has its reason.

4.1 Preparation of sealing material. The Grundfos UPS series delivers the pump with a set of flat rubber seals (O-ring or flat gasket depending on the model). These seals are inserted between the flange surfaces. Never use Teflon tape on flange joints – it is intended for threads, not for flat flange seating surfaces. The rubber gasket does not require lubrication, but you can easily apply silicone grease to ease installation.

4.2 Checking the flow direction. An arrow indicating the flow direction of the medium is engraved or stuck on the pump body. This arrow must point in the same direction as the water flow in the pipe. If you install the pump backwards, it will operate, but with significantly reduced performance and may cause cavitation.

4.3 Mounting the pump. Insert the pump between the flanges of the pipe. Check that the seals are correctly seated in the flange groove and have not shifted sideways. Manually insert the bolts – without tightening – on both sides (inlet and outlet).

4.4 Setting the motor position. Before tightening the bolts, set the motor to the correct position – the terminal box must be facing up or to the side, not down. Grundfos UPS series allow rotating the motor head by 90° without disassembly – loosen the 4 bolts connecting the motor to the hydraulic part and rotate to the desired angle.

4.5 Tightening the bolts. Tighten crosswise in a staggered manner, gradually increasing the torque. For standard flange bolts M8, the recommended tightening torque is 10–15 Nm, for M10 it is 20–25 Nm. If you do not have a torque wrench, as a rough guide: the bolt is tightened when you feel a clear resistance and the gasket is slightly compressed – not deformed.

4.6 Electrical connection. Open the terminal box cover. Grundfos UPS 25-30 and similar models have a three-wire connection: L (phase – brown), N (neutral conductor – blue), PE (protective conductor – green/yellow). Connect the wires to the terminals according to the marking, tighten the cable gland so that the cable is mechanically secured and cannot be pulled out accidentally. Close the terminal box cover.

Step 5 – Filling the system, bleeding air and test run

This is a phase that is often underestimated, and then people wonder why the pump is making noise or why some radiators are cold. Air in the system is the number one enemy of any heating circuit.

5.1 Open the shut-off valves. Slowly open the ball valve on the pump inlet, then on the outlet. Watch the flanges – if there is any dripping, stop, close the valves and reseal.

5.2 Filling the system (if it was drained). Open the filling cock, usually on the boiler or on the lower distribution. At the same time, open the bleed valves on the radiators, starting with those placed highest. Bleed the air until water starts to flow without bubbles.

5.3 Bleeding the pump itself. Grundfos UPS has a bleed screw on the front side of the body (a slotted screw plug for a flat screwdriver). Before the first start, loosen it by half a turn – air will escape with a quiet hissing sound. When water starts to flow (without bubbles), tighten the plug again.

5.4 Pressure check. The pressure gauge on the boiler should indicate 1.0–1.5 bar in a cold system (before heating). If the pressure is lower, add water via the filling valve. If it is higher than 2 bar, check the expansion tank.

5.5 First start-up. Plug in the pump or switch on the circuit breaker. Grundfos UPS 25-30 starts automatically. Listen to the operation – a quiet humming is normal. Knocking, rumbling or strong vibrations indicate air or another problem. Wait 5–10 minutes and check whether the radiators begin to heat evenly.

5.6 Setting the speed level. Grundfos UPS 25-30 has a switch for three speed levels on the sides. For a standard family house (6–10 radiators, 150–200 m of piping), start at level 2. If distant radiators are cold or the pump is humming, increase to level 3. If the noise in the distribution is too high (valve clicking, pipe noise), reduce to level 1.

Typical problems during installation and how to solve them

From experience, I know that most problems during the installation of circulation pumps are repeatable and predictable. Here are the most common ones:

Leak at the flange after filling

Cause: improperly inserted gasket (shifted during installation), insufficiently tightened bolts, or damaged seating surface. Procedure: close the valves, drain locally (remaining water from the pump loop), open the flange, check the gasket and flange surfaces. If the surface is scratched or deformed, either file it down (if it is thick enough) or replace the flange.

Pump hums, but water does not flow (radiators do not heat up)

Most likely cause: air in the pump or in the system. Bleed again – including using the bleed screw on the pump. Another possibility is the wrong installation direction (pump working against the flow). Third – the pump is jammed (rotor is not turning). See the article Grundfos pump does not pump or hums – causes and solutions for a more detailed diagnostic procedure.

Strong vibrations and noise

If the pump vibrates, the problem may be in an asymmetric tightening of the flange (the pump is under mechanical stress – the pipe is "pulling" it to the side), or it is installed on a too thin bracket without vibration dampers. Grundfos sells rubber pads under the flange that significantly reduce the transfer of vibrations into the pipe. Another cause may be that the pipes are not properly secured and they resonate.

Pump does not start – no reaction

Check the circuit breaker and verify that the voltage is present at the pump terminals (using a multimeter: 230 V AC between L and N). If the voltage is fine, but the pump does not react, the problem is in the electronics or the rotor. With Grundfos UPS, it is worth trying to unblock the rotor through the air vent – carefully insert a long flat screwdriver into the rotor slot and try to manually rotate it. If it does not move, it is jammed. More in the article Common Grundfos pump failures and how to eliminate them.

Specifications for installation of Grundfos solar pumps

If you are installing a pump for a solar circuit, different rules apply. Solar circuits operate with glycol (a non-freezing mixture), which has different viscosity properties than pure water and is more aggressive towards standard sealing materials. Therefore, you must:

Use a pump certified for heat transfer media with glycol – for example, Grundfos Solar 25-120 or Grundfos Solar 15-80, which are specifically designed for this purpose.
Use EPDM seals instead of standard NBR rubber – EPDM is resistant to glycol mixtures.
Ensure that the air vent on the solar circuit is placed before the pump (not after it).
Account for temperatures up to 130–150 °C during solar circuit stagnation – the pump must be dimensioned for this.

More detailed information about solar pumps can be found in the article Grundfos solar pumps – what they are used for and how they work. To distinguish them from standard circulators, also read Grundfos UPS vs. Grundfos solar pumps – which one is suitable for your system.

How to set up the pump after installation – optimizing performance

After successful installation and the first test run, comes a phase that most installers skip: properly setting the pump performance. It is a pity, because a properly set pump consumes less energy and is quieter.

Grundfos UPS 25-30 has three fixed speed levels. Basic rule: the pump should operate at the lowest level at which all rooms are evenly heated. Procedure:

Turn on the heating at full power (thermostat to max).
Start at level 1. Wait 30 minutes and check all radiators – are they all warm at the inlet and outlet?
If distant radiators are cold (or their inlet is warm, but the outlet is cold), increase to level 2 and repeat the test.
If the system is balanced and all radiators heat evenly, stay at that level.

In modern systems with thermostatic valves (TRV) and an equithermal control, it is ideal to use a pump with electronic differential pressure regulation (the so-called Autoadapt function in Grundfos ALPHA series) – the pump automatically adjusts its performance according to the system's current needs. Such a solution can reduce energy consumption by up to 50 % compared to fixed-speed pumps.

Annual inspection and maintenance after installation

The Grundfos circulation pump is a wet-rotor type – the rotor is directly washed by water, so it does not require lubrication. Despite this, I recommend performing the following checks once a year:

System air venting (September–October before the heating season) – even a small amount of air increases noise and worsens flow.
System pressure check – a cold system should have 1.0–1.5 bar. If the pressure repeatedly drops, look for leaks or faulty expansion tank seals.
Flange inspection – visually check for signs of leakage (limescale deposits, rust stains).
Manual rotor rotation – if the pump was idle all summer, before the first start, check that the rotor turns freely (through the air vent, as described above).
Electrical connection check – no cracked insulation, no corrosion on the terminals.

A more comprehensive overview of maintenance can be found in the article Maintenance and service of Grundfos pumps – what to check every year.

Frequently asked questions (FAQ)

Do I have to drain the entire system if I have closing valves at the pump?

No, if the valves are functional and sealing well, it is sufficient to close the branches before and after the pump and drain only the local loop (usually less than 2 liters of water). If you are unsure whether the valves are sealing, or if they are not installed at all, drain the entire system – it is a safer procedure. Ball valves are more reliable than old gate valves, which may leak after many years.

Can I replace the pump myself, or do I need a professional?

If replacing with the same type (same flange, same connection), a skilled DIYer can manage it. Complicating factors: working with electrical connections (if you lack experience, it is better to call an electrician at least for the wiring), or if it involves changing the pump type with modifications to the piping (e.g., changing the pipe diameter). In most EU countries, installation of circulation pumps does not require mandatory professional certification – unlike gas installations.

Why does the pump make noise after installation, even though I have bled it?

Possible remaining sources of noise include: a) air still present in the system at other locations (radiators, manifolds), b) too high a speed level – reduce it, c) mechanical stress in the piping (the pipe is pulling the pump sideways) – check the pipe securing, d) unsuitable pump position – motor pointing downward. Noise in solar circuits may also be caused by cavitation at high temperatures – in this case, check the system pressure and add pressure via the expansion tank.

What to do if the new pump does not fit into the space after installation (different dimensions)?

Grundfos UPS 25-30 has a construction length of 130 mm, which is a standard size for most older installations. If the old model had different dimensions, the solution is expansion spacers (extension nipples) or replacement flange kits. Grundfos sells adapter flanges for common sizes. If the dimensions differ significantly (e.g., 180 mm vs. 130 mm), it may be necessary to slightly shorten or extend the piping – in this case, I recommend calling an installer.

How long does the entire installation take?

For an experienced DIYer with prepared valves and a functional system: 1–2 hours including bleeding. If the entire system needs to be drained, add another hour for refilling and bleeding all radiators. In older homes with many radiators (15 or more) and long piping, bleeding may take the entire morning.

Can I install a more powerful pump than the original one?

Theoretically yes, but in practice it may not bring any benefits. An oversized pump causes noise in the piping (popping, humming), increases wear on thermostatic valves, and unnecessarily consumes energy. Always start from the hydraulic calculation of the system – read more about it in the article What Grundfos pump power do I need for my house. Grundfos UPS 25-30 covers most family homes up to 200 m² without overdimensioning.

Conclusion – installation of a Grundfos pump is not rocket science, but it requires preparation

Installation of a Grundfos circulation pump is a task that can be done by yourself, provided you have the right tools, understand the basic principles (flow direction, motor orientation, proper sealing), and especially do not underestimate the safety steps before the actual installation. From dozens of customer cases where I have dealt with problems "after installation," one main conclusion emerges: 90 % of the problems stem from rushed preparation or skipping one of the steps.

If you are unsure which pump model is suitable for you, take a look at the product page of the Grundfos category on atria.sk or read the accompanying articles in the Knowledge Centre – specifically How to choose the right Grundfos circulation pump for heating and Common questions about Grundfos pumps.

And remember: a well-installed and properly adjusted Grundfos pump can reliably serve for 20 years – with one condition: it should be vented every year at the beginning of the season.

Do you have a question on this topic?

Having trouble making a decision or dealing with a specific situation in your home? Write to us – we will be happy to help.